Current methods of determining whether a vehicle is compliant with emission standards include open path and closed path emissions measurement systems. In a closed path system, an emission sensor is directly connected to the exhaust of the vehicle, such as by insertion into a tailpipe. An open path vehicular emissions measurement system collects data by a means other than a direct connection to the tailpipe, such as a remote sensor that analyzes the individual components of emissions. Open path vehicle emission systems are often preferable to closed path systems because they can be used in numerous locations and do not require the vehicle to stop for testing.
Various open path emission sensing systems have been known. One such device uses a radiation source on one side of a roadway that projects a beam across the roadway to be received by a detector. The radiation source and the detector are located on opposite sides of the roadway. The radiation source emits light spectra that may be used to detect an emission signature by way of absorption of light, or which alternatively may be used to excite emission components so as to cause the components to emit light. The detected emission signature can then be used in various applications, such as the measurement of a vehicle's compliance with emission limits and the determination of the type of fuel that a vehicle is using.
A disadvantage of many known arrangements is that the radiation sources and detectors must be placed on opposite sides of the roadway from each other. Since both the detectors and radiation sources require power to operate, this means that a separate power supply must be provided on each side of the roadway. Some known arrangements have tried to overcome this problem by using a radiation source on one side of a roadway and a reflective apparatus on the other side of the roadway.
Furthermore, current open path embodiments are unable to measure particulate matter (PM), as they are equipped to only measure the density, referred to as “opacity”, of smoke emanating from a vehicle's exhaust. Particulate matter is defined to be small solid masses, and include a size of the particle in the symbol for PM. PM10 consists of particles with an aerodynamic diameter of 10 microns or less. PM2.5 consists of particulate matter with an aerodynamic diameter of 2.5 microns or less. Particles less than 1 micron in diameter tend to lodge deep within the lungs, where the fine particles can cause respiratory or heart problems. PM2.5 also impairs visibility. A measurement of opacity historically has not correlated well with actual PM measurements, nor have opacity measurements properly characterized the particle sizes that most affect human health and welfare.
At lease 90% of exhaust particles from gasoline- or diesel-powered vehicles are in the PM2.5 size range. Furthermore, most exhaust particles from these fuels are 0.1 to 0.2 micron or smaller. Exhaust particles consist of unburned fuel, motor oil, and partially burned fuel, known as organic carbon (OC), coated onto soot particles that are known as elemental carbon (EC). For diesel exhaust, elemental carbon comprises about 70% of the total PM mass.
The United States Federal Reference Method (40 CFR 86, Subpart N) for sampling particulate matter requires a vehicle to be connected to a dilution tunnel. The exhaust is transported through an insulated, smooth-walled stainless-steel tube to a constant flow dilution tunnel typically operating at 10-30 cubic meters of flow volume per minute at between 20-30° C. The dilution air flow must be sufficient to prevent water condensation, maintain a diluted exhaust temperature at less than 52° C., and ensure turbulent flow. The exhaust is pumped through a filter that is weighed prior to usage for the emissions test. The filter is weighed after the test and the difference in weight prior to and after the emissions test is the PM mass. Using this method, a laboratory must equilibrate the filters for a long period of time in a constant humidity chamber before weighing them.
Other current art, such as a Tapered Element Oscillating Microbalance (TEOM) system, also requires at least a portion of vehicle exhaust to be channeled through a chamber where the amount and size of particulates of exhaust can be analyzed. The TEOM methodology obviates any filter media, assuming that speciation of the particulates is not desired. Nonetheless, the TEOM methodology requires a vehicle to be taken to a specific testing facility, due to the closed-path nature of its methodology, and requires special plumbing modifications if particulates are to be speciated from filter media.
Studies have found that the current closed path embodiments are accurate for measuring total PM mass but overestimate the number of very small exhaust particles (10-30 nanometers) by a factor of two to four. There are two reasons for the very small particle bias. The particulate matter tends to accumulate on the inside of the hose leading from the vehicle tailpipe to the dilution tunnel, causing very small particles to be released during subsequent tests. And the dilution factor of the dilution tunnel is less than would occur under ambient conditions, which can cause gases such as sulfur dioxide to condense into particles. An open path emissions testing embodiment would not suffer the effects of particulates being scavenged in the testing apparatus itself
Furthermore, current open path sampling art for measuring opacity does not have a good correlation with the Society of Automotive Engineers (SAE) Snap-Acceleration Smoke Test Procedure issued in SAE bulletin J1667. While this SAE J1667 test is for stationary vehicles on a treadmill, it is nonetheless desirable to have a better method for open path emissions sensors to be able to measure and estimate the opacity of a vehicle's exhaust that has improved correlation with the SAE J1667 standard.
Also, current open path emissions sampling art cannot determine if a tested vehicle was burning excessive amounts of lubricating oil from its engine, due to wear of internal sealing components within the engine or other reason. It is desirable to have a system that can determine whether this excessive lubricating oil burning condition is occurring with each tested vehicle.
Accordingly, it is desirable to provide an improved optical transmission, reflection, and detection system that can additionally measure particulate matter along with gaseous emissions measurements, along with an improved correlation opacity measurement as herein disclosed.